Ensure default handler for OTP 21.1+ logger is removed

Author: lukebakken

src/rabbit_lager.erl

@@ -16,7 +16,7 @@
 
 -module(rabbit_lager).
 
--include("rabbit_log.hrl").
+-include_lib("rabbit_common/include/rabbit_log.hrl").
 
 %% API
 -export([start_logger/0, log_locations/0, fold_sinks/2,
@@ -26,9 +26,10 @@
 -export([configure_lager/0]).
 
 start_logger() ->
+    ok = maybe_remove_logger_handler(),
     ok = app_utils:stop_applications([lager, syslog]),
-    ensure_lager_configured(),
-    lager:start(),
+    ok = ensure_lager_configured(),
+    ok = app_utils:start_applications([lager]),
     fold_sinks(
       fun
           (_, [], Acc) ->
@@ -176,6 +177,10 @@ lager_configured() ->
 configure_lager() ->
     ok = app_utils:load_applications([lager]),
     %% Turn off reformatting for error_logger messages
+    case application:get_env(lager, error_logger_redirect) of
+        undefined -> application:set_env(lager, error_logger_redirect, true);
+        _         -> ok
+    end,
     case application:get_env(lager, error_logger_format_raw) of
         undefined -> application:set_env(lager, error_logger_format_raw, true);
         _         -> ok
@@ -348,7 +353,6 @@ generate_handler(syslog_lager_backend, HandlerConfig) ->
     DefaultConfigVal = default_config_value(level),
     Level = proplists:get_value(level, HandlerConfig, DefaultConfigVal),
     ok = configure_syslog(),
-    ok = app_utils:start_applications([syslog]),
     [{syslog_lager_backend,
      [Level,
       {},
@@ -575,3 +579,17 @@ list_expected_sinks() ->
             ok = application:set_env(rabbit, lager_extra_sinks, List),
             List
     end.
+
+maybe_remove_logger_handler() ->
+    M = logger,
+    F = remove_handler,
+    try
+        ok = erlang:apply(M, F, [default])
+    catch
+        error:undef ->
+            % OK since the logger module only exists in OTP 21.1 or later
+            ok;
+        Err:Reason ->
+            error_logger:error_msg("calling ~p:~p failed: ~p:~p~n",
+                                   [M, F, Err, Reason])
+    end.